Research On Preparation And Properties Of New Al-Ti-C-La Master Alloy

The aluminum and aluminum alloy plays a more and more important role in people's life,which makes people more demands on the performance of aluminum.The addition of the grain refiner in the smelting process is a good way to improve the performance of the aluminum.The usual master alloy is Al-Ti-B,but it also has a number of disadvantages,and its use performance is reduced.Al-Ti-C grain refiner,a high-quality refiner,is capable of overcoming the defects of Al-Ti-B,but the Al-Ti-C grain refiner also has the disadvantage that the wettability of the carbon source and the aluminum melt is poor,the poor wettability is difficult to synthesis of TiC.Rare earth is a surface active material,which can improve the wettability of graphite and aluminum melt.In this paper,the new type of Al-Ti-C-La master alloy was prepared by commercial pure Al,Ti powder,graphite powder,Al powder and La₂O₃ powder by aluminum melt in-situ reaction method.The microstructure,preparation process and synthesis thermokinetics of Al-Ti-C-La master alloy have been studied by means of X-ray diffraction?XDR?,scanning electron microscopy?SEM?equipped with energy-dispersive spectrometry?EDS?and transmission electron microscope?TEM?,while the refinement effect on commercial pure aluminum,the refinement mechanism and resisting fading ability of Al-Ti-C-La master alloy were analyzed.In addition,the effect of Al-Ti-C-La master alloy on the microstructure and properties of A356 alloy was studied by applying the Al-Ti-C-La master alloy to A356 alloy.The main contents of the study are as follows:?1?Different kinds of Al-Ti-C-La master alloy prepared by aluminum melt in-situ reaction method had been researched on effect of different preparation temperature and different addition of La₂O₃ on microstructure of Al-Ti-C-La master alloy.The experiment results show that Al-Ti-C-La master alloy mainly consists of Al matrix,lath-like Al₃Ti phase,particle-like or cluster-like TiC phase distributed on Al matrix or grain boundary,and blocky-like or enwrapped-like Ti₂Al₂₀La phase.Adding rare earth oxide La₂O₃ is beneficial to accelerate the formation of TiC in Al-Ti-C system,the morphology of Al₃Ti phase changes from blocky-like or short bar-like to needle-like or lath-like with the increase of the proportion of La₂O₃.In the case of higher temperature,the fine Al₃Ti phase grows into strips or needles,and the TiC phase and the Ti₂Al₂₀La phase can also be combined and grow,and the diffusion of TiC in the aluminum melt is promoted,thereby TiC cluster decreases.?2?The synthesis thermodynamics of Al-Ti-C-La master alloy was studied,the kinetic model of synthesis reaction of Al-Ti-C-La master alloy was established based on the quenching experiment.The analysis of thermodynamic calculation and dynamic process show that:in the preparation process,firstly,Al reacts with Ti to produce Al₃Ti,C reacts with Ti and Al₃Ti to form TiC based on the aluminothermy reaction.Rare earth oxide La₂O₃ and C powder and Ti powder under the action of O₂in the air occurs to produce CO,TiC,[La]atom and LaC₂.[La]atom adsorbs on the Al₃Ti surface to form the new rare earth compounds Ti₂Al₂₀La.?3?The effect of Al-Ti-C-La master alloy on the refinement of pure aluminum and its refining mechanism were studied,while the anti-grain refinement and the decay mechanism of Al-Ti-C-La master alloy on pure aluminum were analyzed.The experiment results show that:Rare earth oxide La₂O₃ is beneficial to enhance the refining properties of Al-Ti-C master alloy.The refining properties of the prepared Al-Ti-C-La master alloy are obviously better than that of the Al-Ti-C master alloy when the content of oxide La₂O₃ is 10 wt%,the reaction temperature is 930?,and the grain size of industrial pure aluminum can reach about 200?m.Compared with Al-Ti-C master alloy,Al-Ti-C-La master alloy has good grain refinement and anti-grain refinement decay property,and it still has better refining effect in 90min.?4?The effect of Al-Ti-C-La master alloy on the microstructure and mechanical properties of A356 alloy was studied.The experiment results show that:When the content of 4#Al-Ti-C-La is 3wt%and the master alloy is added at 770?,the tensile strength,elongation and Vickers hardness of the modified A356 alloy reach the highest values after T6,which can reach 158.8MPa,5.9%,49.8HV,respectively,With the increase of 4#Al-Ti-C-La,the fracture mode changes from cleavage fracture to dimple fracture.When the addition of 4#Al-Ti-C-La is 6wt%and the master alloy is added at 730?,the refining effect is the best,and A356 alloy has the best mechanical properties after T6,its tensile strength is 183.5MPa,and its elongation is8.2%,the Vickers hardness is 62.3 HV.With the increase of 4#Al-Ti-C-La,the fracture mode changes from quasi-cleavage fracture to dimple fracture.